What is the best way to achieve the transparant walls for ALL walls on screen that are not facing the player?

I’ve been searching for days now and only thing I find is how to do partial transparancy based on when your character runs in front of an obstacle or wall.

The game will have a fixed camera point of view so there’s no need to make it adjustable for all sides.
Basicly it will always have the same sides of the model in transparancy (except maybe when it’s rotating or something).

Here is an example of what I mean.

I’m trying desperately to achieve this effect.

If the camera cant rotate, then you could set a script that will change the material of a wall if rotation is z direction or X direction.